Weight lifting is a popular sport and fitness pastime. The popularity of weight lifting has increased significantly in recent years. Weight lifting can serve a number of purposes, including, for example, body building, toning, strengthening, exercise and rehabilitation. A variety of weight lifting styles and strategies have developed. The particular weight lifting styles and strategies for achieving particular ones of such purposes vary. Generally, such styles and strategies take the form of various weight lifting exercises in which particular lifts are employed using particular muscles of the body. The results achieved through a particular style and strategy in weight lifting is thus varied by the particular exercise procedures and methods pursued.
A wide variety of weight lifting exercise procedures and methods have developed. Weight lifting may be accomplished through so-called "free weights", which consist essentially of a weight, generally attached to some form of handle, which the user grasps and lifts by use of particular muscles of the body. On the other hand, numerous weight lifting machine devices have been designed to further particular weight lifting goals.
Weight lifting machine devices take on a variety of styles, shapes and forms. Such devices are typically designed to further particular muscle development goals sought to be achieved by the user through the use of the devices in weight lifting exercises. Certain of such devices tend to be geared towards use in developing particular muscles or particular sets of muscles of the user's body. For example, a number of such devices are directed to use in developing leg muscles of the user, such as knee extension and leg lift machines.
The various mechanical machine devices designed for use in weight lifting typically provide greater ease of use, more efficient weight lifting exercise, and some degree of versatility over traditional free weights. In addition, such machines, in some instances, enable the user, in some measure, to regulate resistance force during particular exercises and also offer other desirable aspects. Regulation of resistance force is in many circumstances advantageous in that the regulation may be used to emphasize resistance at certain points, critical to desired muscle development, during a particular exercise and to de-emphasize resistance at certain other points during such exercise, critical to limit potential injury to muscles or other parts of the user's body. It is, therefore, very desirable to include a mechanism in a weight lifting machine device which provides a varying resistance force during performance of the weight lifting exercises. A design goal for many designers of weight lifting devices is to provide a mechanism for creating such a variable resistance.
Weight lifting machine devices often also employ a lever arm assembly which operates against a resistance force typically provided by sets of weights or other resistance means. Such a lever arm is generally designed to be moveable by the user when weight lifting force is applied by the user to the arm in sufficient magnitude to overcome the resistance force. Though a variety of configurations for weight lifting machine devices are possible, a typical configuration includes a set of weights positioned for upward vertical movement in response to weight lifting force. Additionally, such a machine typically includes a lever arm assembly for application of weight lifting force by the user. The lever arm is generally rotatably movable within a semicircular range. The weights are connected with the lever arm by a cable or chain linkage, such that angular movement of the lever arm is synchronous with vertical, upward movement of the weights. Various pulleys and levers may also be employed with the cable or chain linkage for translating the force and movement of the lever arm to vertical, upward force operating against the resistance force of the weights causing the weights to move vertically and upward.
A recent trend in design of weight lifting machine devices is to direct the designs to particular exercise uses or particular muscle development goals. Improvements have been made in the particular mechanisms employed in such devices to achieve such goals. As an example, it has been determined that users often do not want the lever arm to move in its typical full range of semicircular movement. Further, it has been determined that users will at times prefer to adjust the initial starting position of the lever arm. Designers have recognized these desires of users and have at times incorporated mechanisms for adjusting the starting position and the range of movement of lever arms in such machines. Additionally, it has been determined that preferred weight lifting conditions dictate a variable resistance, rather than constant resistance, against a lever arm through its range of motion. Such a variable resistance mechanism has been incorporated into a number of weight lifting machines by designers.
The adjustable lever arm-variable resistance cam mechanisms exhibited in the prior art weight lifting machine devices present a number of problems in their use. Such mechanisms are often complex involving an aggregation of numerous gears, pulleys, lever arms, chains, cables, and other elements. Further, such prior art mechanisms have often not provided for a variable resistance that is, at each particular angular point of movement of a lever arm, the same, irregardless of initial positioning of the lever arm or of range of semicircular movement thereof. In the prior art, the variable resistance often differs as a result of varied initial positioning of a lever arm. Such differing variable resistance, due to varied initial positioning, may result, for example, from vertical movement and thus different initial positioning of the weights in response to adjustment of the lever arm to such varied initial positions. In addition to such differing variable resistance, such prior art mechanisms have proven breakable, complicated in assembly, costly, and/or combinations of these and a host of numerous other problems.
The present invention is an adjustable lever arm-variable resistance cam mechanism for use in an exercise machine or other lifting device which overcomes the problems presented by the prior art. In providing for such a mechanism, the invention includes a cam allowing for various adjustment of initial positioning of a lever arm attached thereto, which cam, upon initial positioning of the lever arm, is thereby automatically adjusted to create appropriate variable resistance from a weight set linked thereto in response to forcible movement of the lever arm by the user.